Recent years have seen rapid growth in a market of display devices, such as a thin-type television and a projector. These display devices include liquid crystal panels. A light-emitting device which emits white light is provided as a white light source device at the back of the liquid crystal panel. The liquid crystal panel is used as a light modulation element of transmission-type, and forms an image by controlling the transmittance of light irradiated from the light-emitting device. Conventionally, as these light-emitting devices, a cold cathode fluorescent lamp (CCFL) or a super-high pressure mercury (UHP: ultra high performance) lamp has been used. However, with intent to conserve energy and reduce the use of mercury in consideration of environment, as such a light source, recent years have seen development of a light-emitting device in which a semiconductor light-emitting element, such as a light emitting diode (LED), in combination with a phosphor optical element that obtains fluorescent light by converting with phosphor the light from the semiconductor light-emitting element.
There are light-emitting device of (i) a phosphor integral-type in which a semiconductor light-emitting element and a phosphor optical element are disposed on the same package and (ii) a phosphor separation-type in which a semiconductor light-emitting element and a phosphor optical element are disposed at separate locations within a display device.
In both types of the light-emitting device, in the phosphor optical element, fluorescent light from phosphors is emitted omnidirectionally. Thus, there are needs of optical systems which efficiently collect fluorescent light or improving directivity of fluorescent light.
Conventionally, there is a technique for improving efficiency in utilizing fluorescent light. For example, patent literature (PTL) 1 discloses a technique in which a dichroic mirror is disposed between an LED element and resin which includes phosphors to reflect, among the omnidirectionally emitted fluorescent light, the light that travels toward an LED element. The following describes a conventional light-emitting device 1000 using FIG. 14.
As shown in FIG. 14, the conventional light-emitting device 1000 includes: a recessed case 1004 including an opening 1042; an LED element 1002 which is a light source for exciting phosphors and is mounted on an element mounting surface 1040 that is a base of the recess of the case 1004; and a dichroic mirror 1003 provided above the LED element 1002. Furthermore, above the LED element 1002, a phosphor-containing silicone resin 1008 that is a silicone resin including rare-earth activated phosphors, such as YAG:Ce or the like having a particle diameter of 10 to 20 μm, is formed via a silicone resin 1007. The side surface of the recess of the case 1004 (i) is a tilted face 1041 that is formed obliquely with respect to a light-emitting direction of the LED element 1002, and (ii) has a function of reflecting, toward the front direction of the light-emitting device 1000, the fluorescent light emitted from the phosphor-containing silicone resin 1008 together with the light emitted from the LED element 1002.
In the light-emitting device 1000 having the above-described configuration, the light emitted from the LED element 1002 passes through the silicone resin 1007 and enters the phosphor-containing silicone resin 1008. A portion of the light which entered the phosphor-containing silicone resin 1008 is reflected, and another portion of the light is absorbed by the phosphors to be emitted as fluorescent light. The fluorescent light from the phosphor-containing silicone resin 1008 is omnidirectionally emitted, and due to multiple reflections by the tilted face 1041, a dichroic mirror 1003, and the like, and is emitted to outside of the light-emitting device 1000 through the entire surface of the opening 1042.
Furthermore, PTL 2 discloses a light-emitting device that uses, as a light source of a projector, fluorescent light obtained by causing light from an excitation light source to incident on a phosphor light emitting element in which a dichroic mirror and a phosphor are used in combination.